This is Section element which is available only when use Thrive’s theme or Landing Page Template(takeover entire page)
FYI This is what they said when I requested fullwidth content compatibility,
Unfortunately you can only do this with the page section element which is only available with a Thrive Theme, or in a Thrive Landing Page.
We have it logged as a request, but when it comes to 3rd party themes there are some challenges in adding full width page sections. We can add them in our themes and our landing pages because we know exactly how their content area is coded.